MDL-22061 workaround for missing alttext of some emoticons

lib/moodlelib.php

@@ -5905,7 +5905,12 @@ class amos_string_manager implements string_manager {
         $string = $this->load_component_strings($component, $lang);
 
         if (!isset($string[$identifier])) {
-            if ($identifier !== 'parentlanguage' and $component !== 'pix') {
+            if ($component === 'pix' or $component === 'core_pix') {
+                // this component contains only alt tags for emoticons,
+                // not all of them are supposed to be defined
+                return '';
+            }
+            if ($identifier !== 'parentlanguage') {
                 debugging("Invalid get_string() identifier: '$identifier' or component '$component'", DEBUG_DEVELOPER);
             }
             return "[[$identifier]]";

lib/weblib.php

@@ -1628,7 +1628,9 @@ function replace_smilies(&$text) {
         $img[$lang] = array();
         foreach ($emoticons as $emoticon => $image){
             $alttext = get_string($image, 'pix');
-            $alttext = preg_replace('/^\[\[(.*)\]\]$/', '$1', $alttext); /// Clean alttext in case there isn't lang string for it.
+            if ($alttext === '') {
+                $alttext = $image;
+            } 
             $e[$lang][] = $emoticon;
             $img[$lang][] = '<img alt="'. $alttext .'" width="15" height="15" src="'. $OUTPUT->pix_url('s/' . $image) . '" />';
         }